ABSTRACT
Tryptophan hydroxylase 2 (TPH2) catalyzes the rate-limiting step in serotonin biosynthesis in the nervous system. Several variants of human TPH2 have been reported to be associated with a spectrum of neuropsychiatric disorders such as unipolar major depression, bipolar disorder, suicidality, and attention-deficit/hyperactivity disorder (ADHD). We used three different expression systems: rabbit reticulocyte lysate, Escherichia coli, and human embryonic kidney cells, to identify functional effects of all human TPH2 missense variants reported to date. The properties of mutants affecting the regulatory domain, that is, p.Leu36Val, p.Leu36Pro, p.Ser41Tyr, and p.Arg55Cys, were indistinguishable from the wild-type (WT). Moderate loss-of-function effects were observed for mutants in the catalytic and oligomerization domains, that is, p.Pro206Ser, p.Ala328Val, p.Arg441His, and p.Asp479Glu, which were manifested via stability and solubility effects, whereas p.Arg303Trp had severely reduced solubility and was completely inactive. All variants were tested as substrates for protein kinase A and were found to have similar phosphorylation stoichiometries. A standardized assay protocol as described here for activity and solubility screening should also be useful for determining properties of other TPH2 variants that will be discovered in the future.
Subject(s)
Mutant Proteins/metabolism , Mutation, Missense/genetics , Tryptophan Hydroxylase/metabolism , Cell Extracts , Cell Line , Cell-Free System , Escherichia coli , Humans , Models, Molecular , Mutant Proteins/isolation & purification , Phosphorylation , Protein Transport , Solubility , Tryptophan Hydroxylase/chemistry , Tryptophan Hydroxylase/isolation & purificationABSTRACT
OBJECTIVE: Familial Mediterranean fever (FMF) is an autoinflammatory disease common in eastern Mediterranean populations. The most severe complication is the development of secondary amyloidosis. Toll-like receptor (TLR-2) plays a critical role in linking the recognition of microbes to immune activation. We investigated whether the Arg753Gln TLR2 polymorphism affected the development of secondary amyloidosis in patients with FMF. METHODS: We studied 75 patients with FMF, 40 patients with FMF who developed secondary amyloidosis, and 116 healthy controls. TLR2 gene Arg753Gln mutations were analyzed with a polymerase chain reaction-restriction fragment length polymorphism method. RESULTS: The frequency of the Arg753Gln TLR2 polymorphism among the Turkish population was 6%, whereas it was 25.2% among patients with FMF (p < 0.01). The difference of the frequency of the polymorphism between FMF patients with and without amyloidosis was significant: 15/40 (37.5%) and 14/75 (18.6%), respectively (p = 0.02). CONCLUSION: The Arg753Gln polymorphism may affect the severity of this monogenic disease by influencing the innate immune response to pathogens. The presence of the polymorphism may influence the phenotype of FMF in geographic areas where bacterial insult is more common.